Phenol-aldehyde wood bonding adhesives incorporating organic hydroperoxides and having improved curing rates



US. Cl. 260-59 4 Claims ABSTRACT OF THE DISCLOSURE Faster curing ratesand shortened press 'times in the bonding of wood products with phenolicresin adhesives are developed by the addition of small amounts of lowerorganic peroxy-compounds to the resin.

BACKGROUND OF THE INVENTION This invention relates to heat setting,resinous adhesive compositions. More specifically, it relates to hotpress plywood adhesives having improved curing times comprisingphenol-aldehyde resinous condensation products modified with a lowerorganic peroxy-compound.

The preparation and use of adhesive resins prepared from formaldehydeand phenol or urea-like compounds, also known as phenoplasts andaminoplasts, is known in the art. (See for example, The Chemistry ofPhenolic Resins by Robert W. Martin, and Encyclopedia of ChemicalTechnology (1960), vol. X, pp. 335, 860 4, etc., edited by Kirk Othmer.)These resins are applied to surfaces, usually cellulosic, which are tobe bonded, and the surface-forming material so treated is heated andsubmitted to elevated pressures. The foregoing operation is generallyaccomplished in costly mechanical devices, such as a press, and anyreasonable means of shortening the functional requirements, that is,time, temperature and pressure, to any appreciable degree, evenfractionally, makes possible substantial savings per unit of articleproduced.

It is known in the art to add soluble metal compounds, for examplechromates, to the resin as accelerators for the reduction of press timein plywood manufacture and the like (cf. US. 2,612,481). However, formany purposes the presence of metal salts in the bond is undesirable. Inthese and other circumstances an accelerator composed of organicmaterial is more suitable provided that the resulting mixture of resinand accelerator has a reasonable shelf or pot life.

DESCRIPTION OF THE INVENTION It has now been found that the curing timeof phenolaldehyde resinous condensation product adhesives suitable forthe bonding of wood or bondable wood products, such as wood veneer, issubstantially reduced by the addition of an amount of a lower organicperoxy-compound based upon resin in the range of from about 0.1 to 5weight percent. Surprisingly, the addition of minor amounts of theperoxide reduces press times by as much as 25 to 50%. More surprising,in view of the reactive nature of organic hydroperoxides in general, thepot-life of such modified resinous adhesives is not unreasonablyaifected.

DESCRIPTION OF PREFERRED EMBODIMENT In a preferred embodiment of theinstant invention, methylethyl ketone hydroperoxide in about 0.5 weightpercent based on resin is added to an aqueous concentrate of aresol-type formaldehyde-phenol resin, as obtained in the reactioneffected by heating a mixture of formaldehyde and phenol in the molratio of 2.25 to 1, respectively. The resulting B-stage resin containingabout 44% solids, the balance being water, is representative. Organichydroperoxide as noted above is added with efficient mixing to the resinat about ambient temperature. The resulting mixture is applied, forexample, to plywood sheeting in the customary manner as by brush,spraying, or dipping, and the desired number of sheets are stacked andbonded in an ordinary plywood press. Using an unmodified resin for thebonding of plywood veneer to produce /s" plywood, a press time of about4.5 minutes is satisfactory. The above modified adhesive permits areduction of the press time to 3 minutes, i.e., a Sil /3% improvement,for the production of a comparable wood laminate.

By lower organic peroxy-compound is meant by definition t-alkylhydroperoxides, and ketone-peroxides containing at least 3 and less than21 carbon atoms.

By ketone-peroxides is meant the complex reaction product obtained bythe acid catalyzed reaction of concentrated hydrogen peroxide with alower ketone, i.e., C carbon atom content (cf. Organic Peroxides by A.V. Tobolsky and R. B. Mesrobian, Interscience Publishers (1954), pp.41-51).

By bondable wood is meant wood in the form of strips, veneer, meal,sawdust and flour, as well as leached or chemically treated solid woodhaving substantially unimpaired wood cellulose structuralcharacteristics.

Like the phenol-formaldehyde resins described above, the curing timesfor other simple phenolic-aldehyde resins are improved by the instantmodification. Thus all or part of the phenol may be replaced by ortho-,meta-, or paracresol; and all or part of the formaldehyde may bereplaced by acetaldehyde or furfural. By definition, the term simplephenolic-aldehyde resins is intended to encompass these systems.Phenol-formaldehyde resins are preferred.

The amount of peroxy-compound which is desirably used varies. In generalsome increase in cure rate is notable after the addition of as little asabout 0.1 weight percent (based upon neat resin) of the accelerator. Onthe other hand, the use of excessive amounts is undesirable because theresin pot-life can be impracticably shortened. In general, however,satisfactory resin pot-lives are experienced where the added acceleratorconstitutes less than about 5 weight percent based upon resin. Becauseof the relatively high cost of these peroxidic curing accelerators,amounts less than 3 percent are preferred, i.e., from about 0.1 to 3percent.

Representative organic peroxy-compounds useful as curing acceleratorsinclude t-butyl hydroperoxide, cumene hydroperoxide, neopentylhydroperoxide, 2,5-dimethylhexane-2,S-dihydroperoxide, 1,1-diethylpropylhydroperoxide, l,1,2,2-tetramethylpropyl hydroperoxide,methylcyclohexyl-lhydroperoxide, 2-hydroperoxy-2,4-dimethyl-B-pentanone, menthanyl-S-hydroperoxide, teralin hydroperoxide, and thelike tertiaryl hydroperoxides; and also includes peroxides ofmethylethyl ketone, diethyl ketone, di-n-butyl ketone, cyclohexanone,cyclooctanone and the like ketone hydroperoxides. Ketone peroxides areas noted above complex mixtures. For example, methylethyl ketoneperoxide is a complex mixture containing mainly 3) z s) OH) COOCXOOH) 3)2 5),

(CH (C (OOH)COOC(CH3) (C H OOCXOOH) (OOH) 3) 2 5),

(CH (C H )C(OH) (OOH), etc.

Ketone hydroperoxides are particularly preferred accelerators.Commercially supplied ketone hydroperoxides are generally complexmixtures as illustrated above for methylethyl ketone peroxide and may bein the form of ester solutions, for example, dissolved in lower alkylphthalate esters.

Preferred t-alkyl hydroperoxides useful in the instant process are ofthe formula R R R COOH in which at least 2 of the groups are alkylgroups and in which one of these groups may be an aryl group.

RESIN PREPARATION Phenolic resins suitable for use in the preparation ofthe fast curing adhesive compositions of the present invention areprepared by heating a mixture of the phenol and aldehyde (usually aformalin solution) in the presence of a catalytic amount of a mineralacid (HCl or H 80 or base (sodium hydroxide, carbonate etc.). The molratio of phenol to aldehyde is generally in the range 1 to 0.2-4respec-tively. Heating is continued at a temperature in the range fromabout 100 to 270 C. until the A-stage or B- stage resin is produced.

Base catalysis results in a resin called a resol, and the acid catalyzedgenerated resin is called a novolac. Either is suitable for theproduction of the fast curing adhesives herein. In plywood manufactureB-stage resins are preferred. U.S. 2,457,493, Re. 23,347 of Mar. 20,1951, contains a representative description of resin manufacture.

Wood bonding adhesive resins as known in the art are usually extended bythe addition of inert filler materials. These include wood flour, walnutshell flour and the like. As much as 20 weight percent of these fillersand higher can be added to the modified resins of the present inventionwithout seriously affecting the desired result. These fillers add bulkto the resin, thereby facilitating handling and spreading.

In a typical operation for the production of plywood veneer, a 100 partaliquot of peroxy-modified resin ob tained as described above is dilutedwith about 20 parts of water. To this mixture is then added with mixingabout 16 parts of walnut shell fiour until a smooth, lump-free mixtureresults. A layer of filled resin is then applied to both faces of asuitable veneer core, for example a strip of wood veneer. Two veneerfaces, each about /s" thick, are then placed on either side of the:core, and the resulting 3-ply assembly is placed in a press at atemperature in the range from about 130-200 C. at a pres sure in therange from about 150-200 p.s.i. for a period varying in the range fromabout 5 to minutes.

In the following examples a standard research test was 2.5 gram weightis then suspended at the end of a stiff wire in the body of the resin.At the other end, the wire is attached to a reciprocating lever arm.Movement of the arm raises and lowers the suspended weight. As the resinexperiences the time-temperature effect, its viscosity increases until agel viscosity value is reached, and movement of the weight through thesample meets with increasing resistance. When the gelation value isreached, automatic switch-off and recordation of the elapsed time of thetest occurs.

EXAMPLE 1 Preparation of typical phenol-formaldehyde resins (a) A2liter, round bottom flask, equipped with heating and cooling means,stirrer, and a temperature recording means, was charged with 483.6 gramsof 90% phenol (4.63 mols), 746.6 grams of 46.5% formaldehyde (11.6mols), 498.2 grams of water, and 193.6 grams of 50% sodium hydroxide(2.42 mols). Stirring was continued throughout the addition of thereagents and also for the remainder of the reaction. There was animmediate exotherm; and the mixture was cooled at first and then washeated to reach 100 C. in about 30 minutes. It was held at thistemperature for 25 minutes, after which it was cooled to 85 C. Afterminutes at 85 C., 55.6 grams of sodium hydroxide (0.69 mol) and 22.4grams of water were added. The mixture was cooled to C. and held at thistemperature until the viscosity reached a Gardner-Holdt viscosity valueof Y-Z (in about 3 hours) when measured at 25 C. The pH of the resinsolution was 11-12, and it had 42% solids. The purplecolored resinsolution was stored at 4 C. until needed for further experimentation.This resin had a formaldehyde/ phenol mol ratio of 2.5/1.

(b) Another resin was prepared in essentially the same way as in (a)except that the ratio of formaldehyde/ phenol was 2.25/1; the solidscontent was 44%; and the viscosity was T. The portion of this resin notused for blending in succeeding examples was stored at room temperature.

EXAMPLE 2 Gel time determination Resin blends were prepared by adding 3,6 and 12 grams of methylethyl ketone peroxide to 1000 grams (on a dryweight basis) of the resin of Example 1(b). After complete mixing, thetest resins were stored at room temperature. Periodically, theGardner-Holdt viscosity and the gel time a C. were determined. Theresults were as follows:

RESIN PROPERTIES used for the evaluation of the resins. In the test thetime required to gel the test sample is determined at a giventemperature. A charge of 25 grams of the resin formulation is placed ina 6" glass test tube surrounded by a constant temperature bath. The tubeis secured in place. A

This experiment was carried out essentially the same as Example 2 exceptthat 6 and 12 grams of cumene hydroperoxide were intimately mixed with1000 grams of a second batch of resin prepared in the same way as inExample 1(b). The results were as follows:

RESIN PROPERTIES Initially After 1 week After 2 weeks After 4 weeksPeroxide Gel Gel Gel Gel cone, Vis. Time, Vis. Time, Vis. Time, Vis.Time, Example percent ((3-11) (min.) (G-H) (min) (GH) (min.) (Gr-H)(min.)

33 0 T 22 W 21 X 18 Z-Z; 17 3b 0. 6 T-U 20 W 20 X 16 Z 14 3c 1.2 T-U 18W 17 Y Examples 2 and 3 illustrate that modification ofphenolformaldehyde resins by the peroxidic materials of the presentinvention shorten the gel time by 6% to 33% with only a slight increasein the rate of storage viscosity buildup as compared to unmodifiedresins. In the case of cumene hydroperoxide modified resin, the increasein viscosity is the same as that of the unmodified resin. This is adecided advantage where long pot life and short cure times are desired.

EXAMPLE 4 The resin prepared in Example 1(a) was used for the followingtests. The indicated peroxide was mixed with this resin at theconcentrations indicated on a dry solids basis. A tube containing thetest mixtures was placed in the gel time tester with the bath at 100 C.The results were as follows:

Peroxide Gel Cone time Example Name percent minutes EXAMPLE Attempts tomix the resin of Example 1(a) with 30% hydrogen peroxide or with 40%peracetic acid resulted in an immediate and substantial increase inviscosity at room tempertaure. These results indicated an unsatisfactorypot life.

EXAMPLE 6 The test procedure previously described was followed exceptthat the Water bath was maintained at 80 C. instead of 100 C. In thiscase, the resin of Example 1(a) had a gel time of 107 minutes.Methylethyl ketone peroxide and cumene hydroperoxide at a concentrationof 1.2% reduced this gel time to 51 and 75 minutes, respectively. Thesame materials at 3% concentration reduced the time still further to 17and 46 minutes, respectively.

EXAMPLE 7 Preparation and testing of plywood Resorcinol is a well-knownmaterial used by the plywood industry to shorten the time required tocure a phenol-formaldehyde resin. In comparative experiments, plywoodwas made using as an adhesive a phenol-formaldehyde resin modified 'by2.7% resorcinol or by 0.6, 0.4, and 0.2% methylethyl ketone peroxide.The plywood was S-ply, /s thick, prepared at a 3-minute and a 15- minuteassembly time. It was pressed at C. for 4 /2 minutes at psi. pressure.Although the weight of the peroxide used was but a fraction of theweight of resorcin- 01 used, in all cases the peroxide modificed resinperformed at the least as well as the resorcinol modified resin.Strength tests carried out immediately after manufacture and after aboil cycle showed greater than 85% Wood failures and less than 15% glueline failures.

As will be evident to those skilled in the art, various modifications ofthis invention can be made or followed, in the light of the foregoingdisclosure and discussion, Without departing from the spirit or scope ofthe disclosure or from the scope of the following claims.

I claim:

1. The composition obtained by mixing into a phenolformaldehyde adhesiveresin, based upon the resin, from about 0.1 to 5 weight percent of anorganic peroxy-compound selected from the group consisting ofmethylethyl ketone peroxide, l-butyl hydroperoxide, and cumenehydroperoxide, wherein said resin consists essentially of the productobtained from the reaction of phenol with formaldehyde and is selectedfrom the group consisting of resol and novolac resins.

2. The composition as in claim 1 further characterized in that saidadhesive is a resol resin and said added compound is methylethyl ketoneperoxide.

3. The composition as in claim 1 further characterized in that saidadhesive is a resol resin and said added compound is cumenehydroperoxide.

4. The composition as in claim 1 further characterized in that saidadhesive is a resol resin and said added compound is t-butylhydroperoxide.

References Cited UNITED STATES PATENTS 3,281,496 10/1966 Rice et a1.260845 WILLIAM H. SHORT, Primary Examiner H. SCHAIN, Assistant ExaminerUS. Cl. X.R.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ql;59 708 Dated Au 5. 19 2 Invent0 MALCOLM P. STEVENS It is certifiedthat error appears in thqabove-identified patent and that said LettersPatent are hereby corrected as shown below:

Col. 2, line 7, "f0 rexample" should read -for example--.

C01. 4, line 49, "a 100C." should read --at l00C.--.

C01. Example 2d, last column, "13" should read --l3--.

Col. 5, line 3 1, "tempertaure" should read --temperature--.

Col. 6, line 9, "modificed" should read --modified--.

Col. 6, line 25, Claim 1, "l-butyl" should read --tbutyl--.

SIGN ED AND SEALED MAY 2 6 1970 (SEAL) Attest: v EdwardMFletcher. Jr-WIMIAM E. 503mm, 3, Attesfing Offi r Oomissioner o2 Patents

